The World Health Organization estimates that there is currently several hundreds of millions of people suffering from bone and joint diseases, and this figure is projected to increase sharply due to the predicted doubling of the number of people over 50 by the year 2020.
Partial or total joint replacement or resurfacing is currently one of the most popular methods of treating for patients who suffer from bone and joint diseases, such as severe degenerative joint osteoarthritis or arthrosis. For instance, approximately 600,000 osetoarthritis patients worldwide undergo total knee arthroplasty (TKA) every year to relieve their joint pain and to restore their proper knee function with respect to joint loading and kinematics. Uni-compartmental knee arthroplasty (UKA), where only the medial or lateral condyles of the femur and tibia are replaced is also a popular and is a less invasive treatment for certain patients with knee osteoarthritis.
There are several different surgical techniques and forms of implants used for both TKA and UKA. In conventional TKA, for example, the surgeon strives to achieve accurate alignment by adequately exposing the knee joint, properly orientating cutting guide blocks across the exposed aspect of the bones from the anterior side of the knee, and sawing off the worn joint surface by using the block surface or slot to guide the oscillating saw-blade.
To adequately expose the knee joint, the standard approach used is a 25-30 cm skin incision extending proximally from just distal to the level of the tibia tubercle (known as the anterior or midline approach), followed by a medial 20-30 cm parapatellar arthrotomy, which extends superiorly through the quadriceps tendon. Although the extent of the incision allows for lateral evertion and dislocation of the patella, thus exposing most of the structures of the knee joint, dividing the distal third of the quadriceps muscle in this manner can have several potential repercussions for the patient. These include increased pain, blood loss, and time to ambulation (both with and without walking aids), prolonged post-operative hospital stay and rehabilitation, and decreased range of motion and knee strength in daily tasks, such as stair climbing and descending stairs, etc.
Minimally invasive surgical (MIS) techniques have been used only for uni-condylar knee arthroplasty for over a decade, though surgeons have only relatively recently begun to apply the principles of MIS to TKA. In this technique, the knee joint is accessed mainly from the side through a 6-9 cm incision instead of a 20-30 cm incision. Approaching bone cuts medially or obliquely instead of anteriorly circumvents the need to evert the patella and violate the quadriceps. This, in turn, reduces morbidity by reducing the trauma to the extensor mechanism, and improves post-operative knee function, recovery rate and pain.
In TKA, implant alignment and positioning is regarded to be one of the most important surgical variables for the long term success of the operation. Implant alignment and positioning can be described by the degrees of freedom associated with each implant. For the femoral component these include three rotations, namely, varus/valgus alignment, flexion/extension alignment, and internal/external or transverse alignment; as well as three positions, namely, anterior-posterior (AP) positioning, proximal-distal (PD) positioning and medial-lateral (ML) positioning. Most TKA femoral implants include an inner surface comprised of at least five planes. The five cutting planes that must be realized on the distal femur are the interior cut, anterior chamfer cut, distal cut, posterior chamfer cut and posterior cut. Other inner implant geometries consist of curved surfaces.
In order to accommodate these different surgical techniques and implants, there exists several different types of bone-cutting or resurfacing guides. These can range from rigid mechanical jigs, to mechanized systems, to robotic cutting guides. Some of these conventional guides are disclosed in U.S. Pat. Nos. 6,858,032 and 5,228,459; U.S. application publication No. 2005/0055028 and German patent No. DE 203036643, all of which are hereby incorporated by reference in their entireties.
Most of the above conventional systems use some type of template to guide a cutting tool. However, all of these conventional systems suffer from a number of deficiencies and in particular, these systems do not provide all of the following desired features: accuracy with respect to global implant positioning; accuracy with respect to bone cut surface reproducibility; flexibility in terms of implant type; flexibility in terms of inner implant surface complexity, geometry and size; compatibility with minimal access approaches; compactness; simplicity and ease-of use.